Tobramycin is a new aminoglycoside antibiotic with activity against a wide range of bacteria. More than 90% of coliform organisms and Pseudomonas were susceptible in vitro to 5μg/ml of tobramycin. Pharmacokinetic properties of tobramycin in neonates are similar to those of gentamicin. Peak levels of 4μg to 6μg/ml are achieved in serum after a dose of 2.0 mg/kg; it can be given every 12 hours for up to ten days without accumulation. Serum half-life values were inversely related to birth weights and creatinine clearances. It is suggested that tobramycin be used only for the treatment of neonatal infections caused by tobramycin-susceptible gram-negative organisms resistant to both kanamycin and gentamicin. Studies of clinical efficacy and toxicity in neonates are necessary before the drug can be recommended for routine use.